There often arises a need to make information available, either to a general population of users or only to certain individuals. Moreover, it sometimes is desirable to make such information available on a secure basis. For example, one context in which this problem arises is the communication of decryption keys to the particular individuals who are authorized to view corresponding encrypted files, while at the same time taking appropriate measures in an attempt to preclude unauthorized individuals from obtaining such information. In fact, in such situations it often will be advantageous to preclude anyone from obtaining information that he or she does not absolutely require, including secondary information, such as who has been granted access rights to which files. Complicating this problem is the fact that both the information and the people who are supposed to have access to it sometimes change over time.